1. Field of the Invention
The present invention relates to zoom lenses having the vibration compensating function for use in single-lens reflex cameras, video cameras or the like and, more particularly, to a zoom lens whose range of variable magnification is about 3, including favorite focal lengths of from the wide-angle region to a mid-telephoto region and which is constructed in a relatively simple form and has a capability of compensating for shaking of a photographed image caused by accidental vibrations, i.e., the vibration compensating function.
2. Description of Related Art
A great variety of proposals have been made heretofore for the zoom lens whose range contains a focal length equal to the diagonal length of the image frame in the middle region, or the so-called standard zoom lens. Looking only at the construction of the zooming section for variable magnification, a great number of forms, namely, the 2-unit, the 3-unit, 4-unit and the 5-unit forms, are found. These forms of zoom lenses are further classified to two main groups, one of which has a positive lens unit at the most front as viewed from the object side. This positive-lead type is suitable to extend the focal length for the telephoto end with the result of realizing a high range zoom lens. The use of this type, however, tends to increase the number of constituent lens units and also to make complicate the structure of construction of the operating mechanism therefor.
The other group has a negative lens unit at the most front. This negative-lead type, on the other hand, though hardly increasing the focal length for the telephoto end to a very large value, is suited to shorten the focal length for the wide-angle end, that is, to realize either a wide-angle zoom lens, or a standard zoom lens in a relatively simple form.
For such a negative-lead type zoom lens, too, there have so far been made many previous proposals. In particular, with the use of lens units constructed in the 3-unit or 4-unit form, standard zoom lenses corrected well for all the aberrations are realized as disclosed in, for example, Japanese Patent publications No. Sho 60-40605 and No. Sho 63-58326.
In Japanese Patent publication No. Sho 60-40605, the standard zoom lens comprises, in order from an object side, a first lens unit of negative refractive power, a second lens unit of positive refractive power and a third lens unit of positive or negative refractive power. This 3-unit form of standard zoom lens aims mainly at a zoom ratio of 2 or thereabout.
In Japanese Patent publication No. Sho 63-58326, the standard zoom lens comprises, in order from an object side, a first lens unit of negative refractive power, a second lens unit of positive refractive power, a third lens unit of positive refractive power and a fourth lens unit of negative refractive power. This 4-unit form of standard zoom lens aims mainly to increase the zoom ratio to 3 weak.
Meanwhile, as one of zoom lenses having the mechanism for compensating for shaking of a photographed image caused by accidental vibrations during the time when taking a shot, there has been proposed a zoom lens capable of compensating for vibrations by shifting certain of lens units constituting an optical system in directions nearly perpendicular to the optical axis, as disclosed in, for example, Japanese Laid-Open Patent Applications No. Hei 2-35406 and No. Hei 8-136862.
The above Japanese Laid-Open Patent Application No. Hei 2-35406 discloses an example of application of the zoom lens as is suited mainly to leaf shutter cameras. The zoom lens cited here is of the 3-unit form, comprising, in order from an object side, a first lens unit of negative refractive power, a second lens unit of positive refractive power and a third lens unit of negative refractive power. Out of these lens units, the third lens unit is selected to be used in moving in the directions nearly perpendicular to the optical axis, to compensate for shaking of a photographed image.
The above Japanese Laid-Open Patent Application No. Hei 8-136862 discloses another example of application which is suited mainly to the standard zoom lens for the single-lens reflex camera. The zoom lens in the 4-unit form, comprises, in order from an object side, a first lens unit of positive refractive power, a second lens unit of negative refractive power, a third lens unit of positive refractive power and a fourth lens unit of positive refractive power. The second lens unit is made to move in the directions nearly perpendicular to the optical axis, thus compensating for shaking of a photographed image.
In general, the optical systems which make the vibration compensating provision in part or one lens unit thereof by parallel decentering in the directions perpendicular to the optical axis have such an advantage that no more optical part such as a variable angle prism is necessary to use for the purpose of compensating for vibrations, but suffer a problem that, when compensating for vibrations, a larger amount of decentering aberrations is produced.
Further, in the case of application of such a vibration compensating method to, for example, the standard zoom lens, the requirement of retaining good correction of all aberrations even in the vibration compensating state must be fulfilled simultaneously with the requirement of minimizing the bulk and size of the photographing apparatus. So, another problem arises in that more appropriate features or conditions must be set forth for certain optical parameters such as the refractive powers of all the lens units and the power distribution than when the vibration compensating function is not in use.